1. Field of the Invention
The present invention relates to a process for producing an optically active N-protected-azetidine-2-carboxylic acid, which is a useful starting material for producing pharmaceuticals as described, for example, in WO98/50420 or Brain Res., 801 (1-2), p. 158, 1998.
2. Description of Related Art
Enantiomerically pure N-protected-azetidine-2-carboxylic acid such as (S)-N-benzoylazetidine-2-carboxylic acid has been produced by recrystallizing (S)-N-benzoylazetidine-2-carboxylic acid(94% e.e.) as disclosed in WO98/02568. For further derivatization to enantiomerically pure azetidine-2-carboxylic acid or a peptide, however, said compound required cumbersome alkaline hydrolysis and neutralization steps or further step of introducing a suitable protective group.